Method of preparing magnesium oxide impregnated activated carbon

ABSTRACT

A novel impregnated activated carbon, containing from about 1.0 percent to about 15.0 percent by weight of MgO, has been found to be useful in a method of decolorizing a crude vegetable oil or a degummed vegetable oil, and removing organic acids therefrom, as well as in a process for making a refined edible vegetable oil wherein a crude vegetable oil is degummed, passed through the impregnated activated carbon, and subjected to steam distillation at reduced pressure. A novel method of preparing the MgO impregnated activated carbon has also been discovered.

BACKGROUND OF THE INVENTION

The present invention is concerned with a MgO impregnated activatedcarbon and its use in an improved process for making a refined ediblevegetable oil. The present invention is also concerned with a method ofdecolorizing a crude vegetable oil or a degummed vegetable oil, andremoving organic acids therefrom. The present invention also deals witha method of preparing the MgO impregnated activated carbon. Moreparticularly, the improved process of the present invention for making arefined edible vegetable oil comprises the steps of degumming a crudevegetable oil, passing the degummed vegetable oil through a bed ofgranular activated carbon impregnated with from about 1.0 percent toabout 15.0 percent by weight of MgO, and subjecting the treated oil tosteam distillation at reduced pressure.

The vegetable oils to which the present invention is applicable are suchedible vegetable oils as soya or soybean oil, corn oil, cottonseed oil,peanut oil, sesame seed oil, rapeseed oil, olive oil, palm oil, palmkernel oil, coconut oil, and babassu oil, among others.

The improved refining process and treatment methods of the presentinvention have proven especially suitable in refining of soybean oil,and they are, therefore, particularly applicable thereto. Soybean oilis, moreover, the most important vegetable oil produced in the UnitedStates, comprising about 82% of the present total annual vegetable oilproduction. Thus, production of soybean oil in the United States is animportant and extensive industry, with current annual production ofedible soya oil being approximately 9.5 billion pounds. While crudesoybean oil is stable and nonreverting in nature, it has a dark colorand a strong odor and taste which make it regarded as unpalatable inthat state. Consequently, a number of techniques have been employedpreviously in the art to refine the crude soybean oil. The resultingproduct, while initially a light colored oil with a bland and agreeableflavor, in many cases unfortunately reverts by stages to moreunpleasantly flavored forms after standing for a short period of time.

In accordance with the improved refining process of the presentinvention, it is possible to eliminate two conventional refining stepswhich are cumbersome and wasteful. Despite the eliminated steps, the endproduct refined oil is acceptable with respect to prevailing industrystandards for taste, odor, and color, and is, moreover, storage stableover the normal shelf life period of from one to three or more months.The end product refined oil produced in accordance with the presentinvention is thus comparable to oils produced by conventional refiningprocesses in these respects.

The MgO impregnated activated carbon of the present invention is able toremove not only substantial quantities of free fatty acids from a crudevegetable oil, but is also able to remove substantial quantities ofphospholipids and peroxide compounds from the crude vegetable oil.

Free fatty acids, referred to herein generally as organic acids, arepresent in crude vegetable oils and may result, as well, from hydrolysisof the crude vegetable oil responsive to a number of conditions. Thefree fatty acids may be saturated, for example, caproic, lauric,palmitic, stearic, and myristic acids, or unsaturated, for example,oleic, linoleic, and linolenic acids.

Phospholipids, or phosphatides, are lipoid substances that occur incellular structures and contain esters of phosphoric acid. Theaminophosphatides, or lecithins, which are mixed esters of glycerol andcholine with fatty acids and phosphoric acid, are especially common. Forexample, the phospholipid content of crude soybean oil ranges from 1.1to 3.2% by weight, and averages 1.8%.

Free fatty acids are conventionally removed by means of causticrefining, as well as steam distillation under reduced pressure, both ofwhich are described in detail below. Phospholipids are conventionallyremoved by means of degumming, which is also described in detail below.

Use of the MgO impregnated activated carbon of the present inventionprovides not only an improved process for making a refined ediblevegetable oil, but also may provide a method of decolorizing a crudevegetable oil or a degummed vegetable oil, as well as of removingorganic acids from such oils. The present invention thus provides acomplete refining process for producing edible vegetable oils, as wellas more intermediate processes for improving the quality of a crudevegetable oil or degummed vegetable oil with respect to decolorizingthereof and removing organic acids therefrom.

Conventional processes heretofore employed for refining vegetable oils,particularly soybean oil, have employed a number of distinct treatmentsteps. However, most often these have consisted of degumming, alkalineutralization, water washing, bleaching, and deodorizing, employed inthat order. See, for example, U.S. Pat. No. 3,629,307.

1. The step of degumming removes various mucilaginous products,primarily protein or albuminoid substances and phospholipids, from thecrude vegetable oil. These phospholipids, primarily lecithin, cephalinand inositol phosphatide, are primarily responsible for the ratherstrong and bitter flavor and aroma of the crude oil. They areresponsible, moreover, for fouling of processing equipment employed insubsequent refining operations, if they are not successfully removed.The degumming process is primarily carried out at the extraction mill,where alkali refining may or may not be carried out. To a much lesserextent, degumming may be done by the refiner at another location. Ingeneral, the degumming process consists of adequately mixing with thecrude vegetable oil, an organic acid such as phosphoric acid or aceticacid, followed by a little water. The resulting hydrated, mucilaginousglobules are subsequently removed from the oil by centrifuging. The stepof degumming may also be carried out without the use of acid, by simplyadding water. Both types of degumming will be described in more detailhereinafter. While substantially all of the phospholipids should beremoved, to a level at least below 2.0 p.p.m., as phosphorus, it has notbeen considered possible to accomplish such a result by conventionalwater degumming alone. Unless substantially all of the phospholipids arethus removed, a dark colored oil will be produced by decomposition ofthe remaining phospholipids at the elevated temperatures encounteredduring the final step of vacuum steam stripping and deodorizing. Thisdark colored material is very difficult to remove by ordinary refiningor bleaching and imparts an off-flavor to the refined vegetable oilfinal product. In addition, the phospholipids tend to chelate any metalions contained in the vegetable oil being refined, and will tend tocarry these over into the refined oil final product, where they cancause undesired oxidation of the refined vegetable oil final product.Moreover, the phospholipids recovered, particularly lecithin, continueto possess good market value as a by-product for sale in nonrelatedfields, for use, for example, as an emulsifying agent.

Various methods of degumming have been employed in the past, includingthe use of various aliphatic and aromatic hydrocarbon and otherdecompositions which are solvents for the vegetable oil, but nonsolventsfor the phospholipids and other mucilaginous products. Acetone is anexample of a suitable solvent. As the solvent is added to the vegetableoil, the decreased solubility of the phospholipids and other impuritiescauses them to precipitate out of the oil. Separation can then beachived simply by filtration. The separated oil is then treated toremove the added solvent, for example, by distilling under a moderatevacuum. See, for example, U.S. Pat. No. 2,117,776. However, such methodshave the serious drawback of requiring the use of often hazardoussolvents.

The preferred method of degumming for use in the improved refiningprocess of the present invention is one whereby the phospholipids andother mucilaginous products are simply hydrated, precipitated, andseparated, desirably by a continuous process. As before stated, an acidsuch as 85% phosphoric acid is also used before the addition of thewater. The amounts used may vary from 300 to 2,000 p.p.m. by volume ofoil. The amount of water may be from 1.0 to 3.0% by volume. Thetemperature may be from 100° to 160° F. The refining process of thepresent invention may employ either (1) the simple degumming methodusing water alone, (2) the acid degumming method using water and acidtogether, or (3) a combination or sequence of the degumming methods (1)and (2). The mixture is introduced into a continuous centrifuge in whichit is heated and caused to circulate continuously, whereby themucilaginous products are completely hydrated and the aqueous phasecontaining these hydrated mucilaginous products is finally discharged.See U.S. Pat. No. 3,206,487.

2. The second step in the conventional oil refining process is alkalineutralization of the oil to remove free fatty acids and otherimpurities. Usually, this neutralization is accomplished simply bytreating the oil with an aqueous solution of sodium hydroxide or otherstrongly alkaline reagent. The free fatty acids in the oil, generallypresent in amounts of from 0.5 to 3.0% by weight, are removed asprecipitated soaps produced by the reaction of the fatty acids andalkaline reagent. The soap thus formed may be removed by centrifugingand the separated soapstock disposed of in some manner. However,handling of these soapstocks has presented considerable problems to thevegetable oil refiner. Usually, these soapstocks are acidulated and freefatty acids are recovered. Nevertheless, waste-products are producedwhich cannot be readily disposed of without creating problems ofenvironmental pollution. As a final step, the oil is then washed withwater to remove virtually all traces of soap, and the oil is then dryedto remove any dissolved or emulsified water which may be present.

3. The third step in the conventional vegetable oil refining process isbleaching to remove pigments remaining in the oil after the previousrefining steps. Such pigments comprise the carotenoids and chlorophyll,among others. Typically, the bleaching step is carried out under vacuumat a moderate temperature in the range of 210° to 250° F., and in thepresence of an activated earth such as fuller's earth, perhaps admixedwith a lesser amount of activated carbon. After the bleaching has beencarried out, it is necessary to filter out the bleaching earth andactivated carbon and pigment products adsorbed thereon. It has beenfound that during bleaching some free fatty acid products are generatedand that the acid value of the oil is raised to about double thatexisting at the end of the alkali neutralization process.

4. The fourth step in the conventional refining of vegetable oils isdeodorizing. During this step live steam is passed through the vegetableoil while it is maintained under a high vacuum and at elevatedtemperatures. The temperature usually ranges from 460° to 530° F. andthe vacuum is maintained at 4 to 6 mm Hg. The process may require from11/2 to 7 hours. During the process most of the free fatty acidsremaining in the vegetable oil are distilled off. Most of the remainingpigment products are destroyed during this step as well. The acid valueand color of the oil are thus improved, and the odor and flavor are madeacceptable. However, if any appreciable quantity of phospholipidsremains, the elevated temperatures experienced during this step wouldresult in a darkening of the oil. For most vegetable oils it has beenconsidered necessary to utilize both alkali neutralization as well asdeodorization in order to remove most of the free fatty acid content ofthe vegetable oil, as well as to get a bland-tasting and odor freeedible oil.

The conventional deodorizizing step has been improved by variation ofthe parameters involved and other modifications. See, for example, U.S.Pat. No. 3,506,696.

The vegetable oil refining method of the present invention is animprovement over the conventional refining process described in theparagraphs above since it eliminates the conventional alkalineutralization and water washing step, and the conventional bleachingstep. This conventional process step elimination is possible because theimpregnated activated carbon treatment of the present invention reducesthe phospholipid and free fatty acid concentration of the degummed oilsufficiently to result in a final product which is both stable andacceptable from the standpoint of taste, color and odor. In addition,the final product is satisfactory as a consequence of the removal ofother impurities in the oil, especially peroxide compounds, by theimpregnated activated carbon treatment step.

In addition to the conventional refining process described above, other,often more direct, methods have been put forward in the art as improvedmethods of vegetable oil refining. For example, U.S. Pat. No. 2,746,867describes a two step refining process comprising a first step ofcarefully controlled partial degumming by means of hydration, followedby steam deodorizing at a moderate temperature. However, this process isintended to leave at least some of the free fatty acids in the product.Similarly, U.S. Pat. No. 2,117,776 describes a two step processcomprising removal of the phospholipids from the crude oil, preferablyby precipitation with a non-solvent, followed by high vacuum-short pathdistillation of the oil.

As already noted above, it is known to employ activated carbonconventionally as a bleaching agent, that is, as a decolorizing agent toremove various pigment products. When employed as a bleaching agent, theactivated carbon is typically utilized in powder form in a batch orcontinuous batch-type operation. Conventionally, such use takes placebefore the vacuum distillation deodorization step. Nevertheless, the arthas preferred to employ activated clays as bleaching agents rather thanactivated carbons due to their greater cost effectiveness, a result ofthe much greater holding capacity of the activated carbons for thevegetable oil, as compared to the activated clays.

However, it is known to employ activated carbons in various ways invegetable oil refining processes. For example, John P. Harris andBernard N. Glick, in "Crude Cotton Oil Filtration", Oil & FatIndustries, pp. 263-265, September, 1928, suggest activated carbonfiltration of crude cotton oil to remove certain colloids and otherimpurities prior to the conventional refining process. U.S. Pat. No.3,455,975, concerned with a refining process wherein deacidification anddeodorization of glyceride oils is accomplished by distillation in asteam current under vacuum, also discloses decolorization pretreatmentwith artifically activated montmorillonite earth and activated carbon.

Finely divided activated carbon impregnated with, or admixed with, analkaline material has been employed in purification of oils. See U.S.Pat. Nos. 1,105,744, 1,705,824, 1,705,825, and 2,105,478.

The MgO impregnated activated carbon of the present invention representsa novel catalyst composition. U.S. Pat. No. 3,817,874 discloses a methodof forming high surface carbons by treating a porous carbon with MgO,among other materials, followed by heating of the carbon in the presenceof CO₂, and then by washing out of all the inorganic materials, but doesnot teach the impregnated activated carbon of the present invention.

A process for refining edible glyceride oils by treating them withactivated magnesium oxide is disclosed in U.S. Pat. No. 2,454,937.Ordinary magnesium oxide, however, it stated to be inactive, and it issaid that activation may be accomplished by heating the magnesium oxidewith water to about 100° C. for about one hour, filtering, drying andheating in the range of 350° to 500° C. for 3 hours or longer.

In contrast to methods heretofore employed in the art, the method of thepresent invention uniquely provides for a straightforward and efficientmeans of preparing refined vegetable oils having a reduced content offree fatty acids, phospholipids, peroxides and other impurities whichwould result in an unstable product and one unacceptable in color, tasteand odor.

SUMMARY OF THE INVENTION

In accordance with the improved refining process of the presentinvention, crude edible vegetable oils are refined by the successivesteps of degumming, passing of the degummed oil through a bed of MgOimpregnated activated carbon, and subjecting of the thus treatedvegetable oil to vacuum steam distillation and deodorization. An ediblevegetable oil refined by this process will have a reduced peroxidesconcentration level, a reduced final phospholipid content, and a reducedfinal free fatty acid concentration.

In accordance with the method of the present invention for treating adegummed vegetable oil with MgO impregnated activated carbon, the thustreated vegetable oil will have a reduced phospholipid content such thatthe oil will exhibit a negative acid heat break test result; and the oilwill have a reduced free fatty acid content, less than about 0.1% byweight.

For purposes of the present invention, the phospholipid level of thetreated crude vegetable oil or the refined vegetable oil final productis measured in accordance with the acid heat break test. In accordancewith the procedure for this test, 80 ml. of oil to be tested is placedin a breaker and 3 drops of concentrated HCl are added. The oil is thenheated to 500° F. A negative test result is obtained when noflocculation of the oil occurs up to 500° F. A positive test result,indicating higher concentrations of phospholipids, is obtained when theoil darkens and flocculation of the oil occurs at temperatures below500° F.

The free fatty acid concentration of the treated crude vegetable oil orthe refined vegetable oil final product is measured in accordance withAOCS Method 5a-40. This method determines the % by weight of free fattyacids in the oil being tested, by KOH titration, using phenolphthaleinindicator, of the oil dissolved in a 50/50 misture ofethanol/isopropanol or ethanol/toluene.

The degumming step of the method of the present invention may be carriedout using any conventional procedure for removing various mucilaginousproducts, primarily protein or albuminoid substances and phospholipids,from the crude vegetable oil. Typically, the degumming step will reducethe phospholipid content of the vegetable oil to about 200 to 250p.p.m., measured as phosphorus. However, it has been possible to obtainphospholipid levels in this degumming step of the present invention inthe range of from about 50 to about 100 p.p.m. of phospholipids, andeven lower, measured as phosphorous.

The preferred method of degumming the crude vegetable oil in accordancewith the method of the present invention is by simple hydration of themucilaginous product impurities contained in the vegetable oil. Thehydrated mucilaginous products form a precipitate which can beseparated. The amount of water employed ranges from about 1 to about 2%by weight, based on weight of crude vegetable oil to be treated. It hasbeen found that certain agents improve the rate and amount ofmucilaginous product precipitation. For example, certain acids, such asacetic acid and phosphoric acid, have been found to improve theefficiency of the degumming step. These precipitation enhancing agentsare most easily employed by simply adding them before the water employedfor hydration of the crude vegetable oil mucilaginous products (gums).

The degumming step may be carried out at normal temperatures andpressures. However, it is preferred to carry out the step at atemperature of from about 100° to about 160° F.

While separation of the precipitated, hydrated mucilaginous products maybe accomplished simply by filtration, the rate and efficiency ofseparation is greatly improved by the use of equipment which permitscontinuous centrifuging of the hydrated crude vegetable oil gums.Indeed, it is preferred to employ equipment which will provide for highspeed mixing and agitation of the acid, water and vegetable oil mixture,with subsequent centrifugal separation. Thus, pumps or other devices maybe utilized to form an intimate physical mixture or emulsion of thewater and oil, whereby the area of surface contact between the water andmucilaginous products in the oil is substantially increased. Then,centrifugal separators remove the water and hydrated mucilaginousproducts to yield demucilaginated oil.

Desirably, the various types of equipment described above will beutilized in such a way that they operate to provide continuousprocessing of the vegetable oil. Also, multiple cycling of the oil andwater can improve the performance results of the process.

Alternatively, the degumming step may be carried out using steam toreplace the water for hydration of the mucilaginous products in thevegetable oil. The emulsion formed is then separated by centrifuging inthe same manner as for the emulsion formed with water in theconventional process.

Subsequent to the degumming step, there may be employed, desirably, astep of water washing of the degummed vegetable oil, for the purpose ofremoving additional amounts of precipitated mucilaginous products andany contaminants that may have been introduced into the vegetable oilduring the degumming step.

The step of MgO impregnated activated carbon treatment comprises passingthe previously degummed vegetable oil through a bed of granularactivated carbon impregnated with from about 1.0 percent to about 15.0percent by weight of MgO. The use of impregnated granular activatedcarbon in a bed to treat vegetable oil is a basic departure from theconventional use of activated carbons as bleaching agents, where theyare normally employed in powder form and in batch or continuousbatch-type operations, which is a less complicated manner of utilizingactivated carbon than the bed system. However, as has already beenpointed out, the impregnated activated carbon treatment step of thepresent invention has an entirely different objective, and achieves anentirely different result, from the bleaching treatment step in whichactivated carbons have been utilized in the past.

By using a bed of impregnated granular activated carbon, it is possibleto achieve an acceptably small effective dosage of carbon for a givenquantity of oil to be treated, by reason of the possibility ofregeneration of the granular activated carbon, and also by reason of thesignificantly lower effective equilibrium concentration adsorptionlevels which exist in a bed of granular activated carbon as compared topowdered activated carbon used in a batch-type operation. Thus,phospholipids could not be removed from degummed vegetable oils to theextent achieved by the activated carbon treatment step of the presentinvention by use of powdered activated carbon in the amounts normallyemployed in conventional batch-type bleaching operations.

The granular activated carbon which may be employed as the basis for theimpregnated activated carbon of the present invention should fall withinthe mesh size range of 12 × 40, U.S. Sieve Series. However, the size ofthe activated carbon granules is not especially critical, so long as itdoes not vary considerably from the indicated range. The activatedcarbon material itsel should be a conventional liquid phase activatedcarbon prepared from any suitable source, including petroleum, coal,wood and other vegetable raw materials. Coal based activated carbonshave been found especially suitable. A preferred granular activatedcarbon material for use as the basis for the impregnated activatedcarbon of the present invention is CAL 12 × 40, available from thePittsburgh Activated Carbon Division of Calgon Corporation.

Magnesium oxide, MgO, is insoluble in water and cannot, consequently, beimpregnated into an activated carbon substrate simply by means of anaqueous solution followed by drying. Furthermore, it is essential topreparation of the impregnated activated carbon of the present inventionthat the MgO be formed or placed within the pore structure of theactivated carbon. Accordingly, it has been discovered that thisobjective can be obtained by use of the particular preparation method ofthe present invention. This preparation method comprises the followingsteps: (a) admixing the activated carbon to be impregnated with anaqueous solution of a sufficient amount of a water soluble magnesiumsalt, preferably MgCl₂. 6 H₂ O, to result in from about 1.0 to about15.0% by weight of MgO in the final activated carbon product; (b) dryingsaid mixture; (c) admixing with the dried product of the previous stepan aqueous solution of a stoichiometric amount of NaOH; (d) drying saidmixture; (e) calcining the product of the previous step at a temperatureof from about 550° to about 650° F. in an inert atmosphere for fromabout 0.25 to about 1.0 hour; (f) water washing the product of theprevious step until the sodium ion concentration of the wash effluent isless than 1.0 parts per million; and (g) drying the product of theprevious step to recover the final product.

It will be appreciated that other water soluble magnesium salts, inaddition to MgCl . 6H₂ O, may be used with good results. For example,magnesium acetate, magnesium phosphate, magnesium borate, magnesiumchlorate, magnesium chromate, magnesium nitrate, and magnesium sulfateare suitable.

The size of the column vessels used to establish the bed of MgOimpregnated granular activated carbon may be varied in size, depending,essentially, on the volume of vegetable oil to be processed.

The total contact time of MgO impregnated granular activated carbon withthe vegetable oil being treated may be from about 4 to about 24 hours,and preferably will be from about 6 to about 12 hours.

The preferred manner of employing the bed of MgO impregnated granularactivated carbon in the process of the present invention is thepulse-bed system. This system duplicates the action of a large number offilters in series in a clean, continuous, closed system. In this system,a small amount of spent activated carbon is removed (slugged) from thebottom of each column once during every eight-hour period. The removedactivated carbon is then regenerated for further use. At the same timethat the spent activated carbon is removed from the bottom of eachcolumn, a corresponding amount of regenerated or virgin activated carbonis added to the top of each column bed from charge tanks located aboveeach column.

The columns themselves are typically cone-bottomed columns ten feet indiameter and thirty feet in height, capable of holding approximately2700 cubic feet of MgO impregnated granular activated carbon. A numberof such columns would be required to process the normal output of asizeable vegetable oil refinery, for example, approximately 60,000pounds of vegetable oil per hour. Clearly, however, the dimensions ofthe columns are not especially critical and may be considerably variedto conform to space requirements or other considerations.

The spent carbon which has been removed from each column is carried bygravity to an oil recovery tank where oil is removed from the spentactivated carbon by washing with a C₅ to C₈ aliphatic hydrocarbonsolvent, particularly hexane. It has been found that hexane is auniquely suitable solvent for removal of the vegetable oil trapped inthe spent activated carbon since the impurities absorbed on theactivated carbon are not eluted with the solvent. Hexane is alsonon-toxic, relatively inexpensive, and readily available. Several bedvolumes washing with hexane will be sufficient to remove substantiallyall of the oil trapped in the spent activated carbon. In turn, removalof the hexane solvent from the activated carbon is readily accomplishedusing steam.

After oil recovery from the spent activated carbon, regeneration iscarried out. The spent activated carbon is conveyed away from the siteof steam stripping to remove hexane by means of a dewatering screw toremove excess water. The spent activated carbon is carried into amultiple hearth furnace where it is regenerated as it passes through acontrolled atmosphere at high temperatures. The regenerated carbon isthen ready for reuse in the overall process.

A unique advantage of the MgO impregnated activated carbon of thepresent invention is its relative immunity from deterioration ordestruction during high temperature regeneration processes. This resultsfrom the high temperature of volatilization of the MgO, which preventsit from being removed from the activated carbon through decomposition,or otherwise. As a result, it is usually unnecessary to reimpregnate theMgO impregnated activated carbon after regeneration.

Before the regenerated carbon or virgin MgO impregnated activated carbonis placed in the column vessels for use, it usually is necessary todeaerate the activated carbon during a preliminary wetting step. It hasbeen found that air bubbles trapped between the granules of activatedcarbon interfere in a material way with the efficiency of the activatedcarbon treatment step. The air bubbles adhere rather tenaciously to theactivated carbon granules, but it has been found that they can besatisfactorily removed by agitation of the activated carbon granulestogether with heated degummed vegetable oil in a preliminary step.

After the step of MgO impregnated activated carbon treatment of thedegummed vegetable oil, the third step of deodorizing is carried out.The deodorization is accomplished by steam distillation under vacuum inaccordance with well known procedures already established in the art.The distillation is generally carried out at temperatures in the rangeof from about 400° to about 550° F., preferably at temperatures of fromabout 460° to about 530° F. The distillation is carried out at a reducedpressure of from about 1 to about 10 mm Hg., preferably at from 4 to 6mm Hg.

Vacuum steam distillation deodorization takes advantage of thesignificant differences in volatility between the basic triglyceridecomponents of the vegetable oil and the various substances which givethe oil its natural odor and flavor. Thus, the relatively volatile odorand flavor causing substances in the vegetable oil are stripped from therelatively nonvolatile oil during the process of steam distillation. Thefunction of the steam in the distillation process is the conventionalone of serving as a carrier for the odor and flavor causing substancesbeing distilled from the oil. There is ordinarily no intended chemicalreaction of the steam with the oil or its components. The steamdistillation is usually carried out at high temperatures in order toincrease the volatility of the odor causing substances in the oil.Carrying out the steam distilation process at significantly reducedpressure protects the oil from undue hydrolysis by the steam and fromatmospheric oxidation. It also greatly reduces the quantity of steamrequired for the process.

Deodorization by steam distillation also significantly reduces the colorof the processed vegetable oil, since the cartenoid pigments responsiblefor the major portion of the oil color are unstable to heat.

Along with odor, flavor and color causing substances, the steamdistillation process also more or less completely removes the free fattyacids in the vegetable oil. The free fatty acid content of the oil canbe reduced by the deodorization process to a level in the range of fromabout 0.03 to 0.015% by weight, which is approximately the same levelachievable by conventional alkali refining. However, since the freefatty acid distillation rate is concentration dependent, and since thedistillation process results in splitting of some oil to form additionalquantities of free fatty acids, and equilibrium point is reached,resulting in a minimum content of free fatty acid in the oil. Thus, useof MgO impregnated activated carbon in accordance with the presentinvention, by substantially reducing the free fatty acid content of thevegetable oil before the step of deodorization by steam distillation,not only reduces the extent of the deodorization process required, butalso can reduce the minimum content of free fatty acid in the oil whichcan be achieved. Moreover, the MgO impregnated activated carbon of thepresent invention can also remove other organic acids, for examplephosphoric acid, which may be present in the vegetable oil.

DETAILED DESCRIPTION OF THE INVENTION

An appreciation of the method of the present invention for preparing theMgO impregnated activated carbon will be gained from the followingExample, which serves to illustrate the manner of carrying out thatmethod.

EXAMPLE 1

A solution of 26.7 g. of MgCl₂.6H₂ O in 100 ml of distilled water wasadded to 100 g. of CAL 12 × 40 mesh U.S. Sieve Series activated carbonhaving an apparent density of 0.522. The activated carbon and MgCl₂.6H₂O solution were mixed and then air dried overnight. A solution of 10 g.of NaOH in 100 ml of distilled water was then added to the air driedcarbon and thoroughly mixed therewith. The mixture was then air and ovendried at 100° C. overnight. The dried carbon was then calcined at 600°F. under a N₂ atmosphere for one-half hour. Before calcining, the driedcarbon weighed 128.7 g., and after completion of the calcining, weighed109.8 g., thus experiencing a weight loss of 18.9 g. during thecalcining process. The apparent density of the carbon after calciningwas 0.586.

After calcining, the carbon was subjected to water washing to removeNaCl. One bed volume was 167.3 cc. and the water washing was carried outusing deionized water at the rate of 1673 cc./hr., or 28 cc./min. TheNa.sup.⊕ concentration of the effluent was measured, with the followingresults:

    ______________________________________                                        Bed                                                                           Volumes    1       5     10  12   15   20  25  30  35                         ______________________________________                                        Na.sup.⊕  Con-                                                            centration                                                                    (p.p.m.)   20,000  35    3.0 2.25 1.65 1.2 0.8 0.6 0.6                        ______________________________________                                    

For comparision, water washing was carried out by soaking of the carbonovernight in different bed volumes of deionized water. The followingresults were obtained:

    ______________________________________                                        Bed Volumes      1        5         10                                        ______________________________________                                        Na.sup.⊕ Concen-                                                          tration (p.p.m.) 5.5      0.85      0.4                                       ______________________________________                                    

After water washing, the MgO impregnated activated carbon was placed inan oven at 100° C. until dry. The apparent density of the impregnatedcarbon was 0.561, and the impregnated amount of MgO was 5.0% by weight.

EXAMPLE 2

The MgO impregnated activated carbon prepared as described in Example 1was evaluated with respect to its efficiency in removing bothphospholipids and free fatty acids from a sample of degummed soya oil.The degummed soya oil was divided into aliquots and passed throughcolumns containing different loadings of MgO impregnated activatedcarbon to result in dosages of 1.0, 3.0, 5.0 and 10.0 g. of carbon per100 g. of soya oil. A total contact time of 4.0 hours was employed andthe process was carried out at a temperature of 93° C.

Phospholipid removal was measured by the conventional acid heat breaktest. For this evaluation, an 80 ml sample of oil was placed in a beakerand 3 drops of concentrated HCl was added to the oil. The oil was thenheated to 500° F. using a Bunsen burner. The oil was observed for theformation of "break", that is, the deposit of impurities, primarilyphospholipids and other mucilaginous materials, in the form offlocculent particles. A negative test result was obtained when noflocculation occurred at temperatures up to 500° F. A positive testresult was obtained when flocculation occurred at temperatures of lessthan 500° F. In addition, the temperature at which flocculation occurredwas noted. The following table of values illustrates the resultsobtained:

    ______________________________________                                        Dosage                                                                        (g. of MgO                                                                    impregnated                                                                   activated                                                                     carbon/100 g.                                                                              Test      Temperature of                                         of soya oil) Result    Break Formation (° F.)                          ______________________________________                                        Blank        +          454                                                   1.0          +          480                                                   3.0          -         >500                                                   5.0          -         >500                                                   10.0         -         >500                                                   ______________________________________                                    

Free fatty acid removal was measured in accordance with the proceduresdescribed in AOCS Method 5a-40. Following these procedures, samples oftreated soya oil were titrated with a KOH solution, usingphenolphthalein as a neutral point indicator. Before titration, the oilsample was dissolved in a 50/50 mixture of ethanol/toluene. The resultsof the evaluation are illustrated in the following table of values:

    ______________________________________                                        Dosage                                                                        (g. of MgO                                                                    impregnated acti-                                                             vated carbon/100 g. Free Fatty Acid                                           of soya oil)        (% by weight)                                             ______________________________________                                        Blank               0.239                                                     1.0                 0.172                                                     3.0                 0.132                                                     5.0                 0.090                                                     10.0                0.042                                                     ______________________________________                                    

The MgO impregnated activated carbon of the present invention providesimproved results over those which can be obtained using either aphysical mixture of MgO and activated carbon, or the activated carbonalone. The MgO impregnated activated carbon of the present inventionalso provides results which are comparable to those which can beobtained using a NaOH impregnated activated carbon, as has beensuggested heretofore in the art. And, the MgO impregnated activatedcarbon of the present invention is not affected by the high temperaturesencountered in thermal regeneration processes, as would a NaOHimpregnated activated carbon.

In order to illustrate the comparative performance of the MgOimpregnated activated carbon of the present invention, its ability toremove phospholipids and free fatty acids was evaluated along with theabilities of virgin activated carbon, caustic impregnated carbon, and aphysical mixture of MgO and activated carbon, to remove phospholipidsand free fatty acids. The comparison is described in the followingExample.

EXAMPLE 3

Samples of degummed soya oil were contacted with varied amounts of testcarbons sufficient to give dosages of 1.0, 3.0, 5.0, and 10.0 g. of testcarbon per 100 g. of soya oil. The following test carbons were employed:(1) the MgO impregnated activated carbon of the present inventioncontaining 3.6% by weight of MgO; (2) virgin CAL 12 × 40 mesh activatedcarbon; (3) 12 × 40 CAL impregnated with 5% by weight of NaOH; and (4)Cane CAL^(R), available from the Pittsburgh Activated Carbon Division ofCalgon Corporation, consisting of a physical mixture of 12 × 40 mesh CALactivated carbon and about 7.0% by weight of MgO. The total contact timeof soya oil and test carbon was 4.0 hours and the treatment was carriedout at 93° C. The test carbon was removed from the treated samples bysuction filtration on a Buchner funnel using Whatman #3 for the top, andWhatman #42 for the bottom filter papers. Measurement of phospholipidremoval was by means of the acid heat break test, described in Example2; and measurement of free fatty acid removal was by means of AOCSMethod 5A-40, also described in Example 2. The results of thecomparative evaluation are set out in the table of values below.

    ______________________________________                                                   Dosage (g. adsor-                                                                          Free Fatty                                                                              Acid-Heat                                              bent/100 g. soya                                                                           Acid (% by                                                                              Break Temp.                                 Adsorbent  oil)         weight)   (° F.)                               ______________________________________                                                   Blank        0.239     462                                         MgO impreg-                                                                              1.0          0.172     484                                         nated CAL  3.0          0.132     >500                                                   5.0          0.090     >500                                                   10.0         0.042     >500                                        Virgin CAL Blank        0.235     455                                                    1.0          0.223     470                                                    3.0          0.211     464                                                    5.0          0.201     472                                                    10.0         0.182     >500                                        5% NaOH    Blank        0.235     455                                         impreg-    1.0          0.063     464                                         nated CAL  3.0          0.027     >500                                                   5.0          0.020     >500                                                   10.0         0.017     >500                                        Cane CAL.sup.®                                                                       Blank        0.239     462                                                    1.0          0.219     463                                                    3.0          0.209     466                                                    5.0          0.199     490                                                    10.0         0.188     >500                                        ______________________________________                                    

An appreciation of the various stages of the treatment steps of theimproved refining process of the present invention can be gained fromthe detailed description which follows.

EXAMPLE 4

Crude soybean oil as available from an extraction plant is usuallyprocessed further at that location, for recovery of lecithin.

In this process, water is the sole degumming agent. The crude soybeanoil from an extraction plant is at a temperature of 125° F. in a storagetank. The phosphorus content is 650 p.p.m., which corresponds to aphospholipid content of 1.95%. It is then pumped through a line at arate of 30,000 pounds per hour, and water is metered into this line by awater flow controller at a rate of 1.0% or 300 pounds per hour. Theinitial mixing of water and oil is done in a pump. The mixture is pumpedat a pressure of 120 PSIG into another line where, a flow control valveis regulated for a flow rate of 30,000 pounds of crude soybean oil andwater. The mixture is then pumped upward into a mixer which is equippedwith a 2 H.P. motor drive and two 14 inch diameter three-bladedpropellers operating at 180 R.P.M. There are two horizontal baffles forthorough mixing.

The agitated mixture of oil and water then flows by way of another lineto a De Laval SRG 214 centrifuge operating at a speed of 4,400 R.P.M.The partially degummed soybean oil flows into another line where theback pressure on this oil phase is controlled by a back pressurecontroller and then flows into a storage tank. The separated wet gumsflow into a line where the back pressure is controlled by a backpressure controller, and then into a tank. The back pressure controllersare of known type and automatically control the operation of theseparator.

The partially degummed oil has a phosphorus content of 200 p.p.m. whichcorresponds to 0.6% of phospholipids. The quantity of wet gums is 900pounds per hour or 3.0% of the oil feed. The analysis of the wet gums is33% water, 45% phospholipids and 22% soybean oil. The wet gums are thenfurther processed for making commercial lecithin. The yield of partiallydegummed oil is 29,400 pounds per hour or 98% yield on a dry basis.

A more complete degumming of crude soybean oil may be achieved by aciddegumming as illustrated in the following example.

EXAMPLE 5

The feed material is the partially degummed crude soybean oil fromExample 4 which contains 0.6% phospholipids. It is pumped to a heaterwhere it is heated to a temperature of 140° F. The pressure in the lineto the heater is 130 PSIG. A flow control valve is set to regulate theflow rate at 29,400 pounds per hour for the oil leaving the heater. Intothis oil a supply of 85% phosphoric acid is metered with a metering pumpat a rate of 0.12% or 34.8 pounds per hour. This equals 0.10% on a 100%acid basis. The oil-acid mixture then flows into a mixer which issimilar to the mixer described in Example 4, except that it is ofstainless steel construction and there is only a 1 minute retentiontime. The flow is then into a line where a water supply thereto isregulated by means of a flow control valve to supply 3% of water or 882pounds per hour. The flow is then into a mixer which is similar to themixer in Example 4, and then into a centrifuge which is similar to thatemployed in Example 4. The wetted gums flow into a tank through anautomatic back pressure valve. The amount of wet gums is 1,285 poundsper hour containing 70% water, 10% phospholipids and 20% crude soybeanoil. It is processed further or otherwise disposed. The degummed oil ispumped through a line provided with an automatic back pressure valve.The pump has an automatic equalizer. The pump pressure is 120 PSIG. Theflow then is to a heater in which the oil is heated to 180° F. Aseparate pipe line supplies hot softened water at 190° F. to the oil,and the flow is controlled by a flow control valve at a rate of 20% or5,800 pounds per hour. The oil and water mixture is then separated in acentrifuge. The wash waters flow into a waste water tank through anautomatic back pressure valve. The washed oil flows into a tank throughan automatic back pressure valve. The washed oil yield is 29,014 poundsper hour containing 0.3% moisture and 60 p.p.m. of phospholipids,measured as phosphorus. The dry weight is 28,927 pounds per hour.

EXAMPLE 6

The degummed soya oil, treated in accordance with the procedures of anyof the preceding examples, is next subjected to the MgO impregnatedactivated carbon treatment step of the present invention. Degummed soyaoil is carried to a pre-filter feed tank where it is stored untilpre-filtration and subsequent processing is carried out. At that timethe degummed soya oil is pumped to a pre-filter, which may be of anyconstruction suitable for removing suspended particulate matter from thedegummed oil. A paper filter may be employed. The sludge of removedsuspended particulate matter is eliminated. The pre-filtered oil is nexttransported to an adsorber feed tank, which is insulated. If necessary,the oil may be refiltered. The oil is now ready for passage through theactivated carbon adsorbers and is pumped through lines to a series ofadsorber columns. The number of adsorber columns employed will varyaccording to the volume of oil being processed. The adsorber columns areinsulated as well as being heat traced, primarily at the bottom conicalportion, for example by small steam lines. After passing upwardlythrough the activated carbon adsorption columns, the oil is thentransported to a post-filter feed tank. If additional activated carbonadsorption treatment is required, the oil may be transported back to theadsorber feed tank. From the post filter feed tank the oil is pumped toa post-filter which is similar in construction to the prefilter and isespecially suitable for removing any activated carbon fines which mayhave become entrained in the oil during passage through the activatedcarbon adsorber columns. The sludge of removed fines is eliminated. Thepost-filtered oil is now ready for the final step of steam distillationdeodorization and is transported to the apparatus for carrying out thisstep.

The adsorber columns are operated as pulse beds and so require continualremoval of exhausted or loaded activated carbon for reactivation, and acorresponding continual replenishing of fresh MgO impregnated activatedcarbon for the adsorber column. Fresh activated carbon, either virginMgO impregnated carbon or reactivated MgO impregnated carbon, issupplied to each of the adsorber columns through insulated charge tanks.In these charge tanks the activated carbon is mixed with previouslyrefined oil. This refined oil is carried to a refined oil storage tankfrom a location elsewhere in the process stream suitable for providingrefined oil. The refined oil is pumped to each of the charge tanks.Fresh MgO impregnated activated carbon is introduced into the chargetanks. The charge tanks are pressurized by a pressurizing medium whichis preferably compressed air, but may be, for example, nitrogen. Thecharge tanks are vented through a line.

After the MgO impregnated activated carbon is loaded, that is, exhaustedby adsorption to practical capacity, it is removed from the adsorbercolumns and carried to a product recovery column which is vented. Theproduct recovery column is insulated and pressurized. A fraction of theoil is transferred under pressure to the adsorber feed tank. Then theremaining oil is removed from the MgO impregnated activated carbon byupflow desorption with hexane supplied from a hexane storage tank. Themixture of oil and hexane is recovered from the product recovery column.This mixture is carried to a hexane/oil storage tank. This hexane/oilmixture may subsequently be removed to an extraction plant or otherlocation where the hexane and oil are, in turn, separated. The hexaneis, in turn, removed from the MgO impregnated activated carbon by steamstripping. The steam is introduced into the product recovery column andthe mixture of steam and hexane is carried away from the productrecovery column. The hexane is recovered from the steam and hexanemixture by condensing of the mixture in a condenser cooled by water. Thehexane is decanted and carried to the hexane/oil storage tank. Theseparated water is sewered.

The desorbed MgO impregnated carbon is now ready for reactivation and istransported from the product recovery column to a desorbed carbonstorage tank. The desorbed carbon is transported as a slurry, preparedfrom water, and the slurry is then dewatered in a dewatering screw,after which the carbon is introduced into a reactivation furnace. Thefurnace is supplied with fuel and combustion air. Steam is also utilizedand is supplied through a separate line. Air for cooling is supplied tothe furnace through a pump. The by-products of the reactivation arefirst treated in an afterburner. They are then removed to a scrubbersupplied with water which is then sewered. Innocuous final products areexhausted to the atmosphere by means of an induction fan. Afterreactivation, the MgO impregnated carbon is carried to a cooler whichemploys water as a cooling medium, with the aid of a water cooler andpump. After cooling, the MgO impregnated reactivated carbon is carriedby means of a reactivated carbon transfer elevator to the charge tanksfor the series of adsorber columns.

EXAMPLE 7

The degummed and MgO impregnated activated carbon treated soya oilprepared in accordance with the procedures of the preceding Examples isnow ready for the final step of steam distillation deodorization undervacuum.

The distillation is carried out at approximately 500° F. and at areduced pressure of approximately 1.5 mm Hg. The distillation is carriedout for appoximately four hours while steam is supplied to the oil atthe rate of 10 pounds per minute. The recovered oil is of acceptabletaste, odor and color, and has a phospholipid content, measured asphosphorus, of less than 5.0 p.p.m.

What we claim is:
 1. A method of preparing an activated carbonimpregnated with from about 1.0 percent to about 15.0 percent by weightof magnesium oxide, comprising:(a) admixing the activated carbon to beimpregnated with an aqueous solution of a sufficient amount of a watersoluble magnesium salt to result in from about 1.0% to about 15.0% byweight magnesium oxide in the final activated carbon product; (b) dryingsaid mixture; (c) admixing with the dried product of the previous stepan aqueous solution of a stoichiometric amount of sodium hydroxide; (d)drying said mixture; (e) calcining the product of the previous step at atemperature of from about 550° to about 650° F. in an inert atmospherefor from about 0.25 to about 1.0 hours; (f) water washing the product ofthe previous step until the sodium ion concentration of the washeffluent is less than 1.0 part per million; and (g) drying the productof the previous step to recover the final product.
 2. The method ofclaim 1 wherein the water soluble magnesium salt is magnesium chloridehexahydrate.